Definite pole alternator



y 1938. L. H. PALMER 2,117,991

DEFINITE POLE ALTERNATOR Filed March 7, 1936 \NvENToR H. Pa/mer Zeray MW ATTORNEY Patented May 17, 1938 UNITED I STATES PATENT OFFICE '6 Claims.

This invention relates to a definite pole alternator.

Such alternators in general have been in cornmon use for a long time. They usually involve a stationary armature and a rotating field structure, excited by. direct current. Difiiculties in the design of such alternators are inherent when the problem of regulation is considered. As the load increases, the armature reaction increases; and its effect in turn depends upon the power factor. This reaction results in a modification of the effective field magnetism, and there is usually a decided drop in the generated electromotive force as the load increases. It has been customary in the past to provide some means for compensating for this drop, which can be operated to vary the field excitation.

It is one of the objects of this invention to reduce very materially the effect of this armav ture reaction and thereby to ensure good regulavarying the air gap is very small can be operated with very little reduction in the electromotive force at full load. It is believed that this effect is due to the very low magnetic reluctance in that path which includes the pole pieces, as compared with the path intermediate the pole pieces.

Accordingly, it is another object of this invention to provide a definite pole alternator in which the magnetic circuit is designed to provide a magnetic reluctance through the pole pieces that is very low as compared with a path intermediate the poles. I

This invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of one embodiment of the invention. For this purpose there is shown a form in the drawing accompanying and forming part of the present specification. This form shall now be described in detail, illustrating the general principles of the inventlon;- but it is to be understood that this detailed de- "as having six poles.

Figure 1 is a front elevation of an alternator embodying the invention, some of the parts being broken away and a part of the rotating field structure being in section;

Fig. 2 is a vertical sectional view taken alon the plane 2-2 of Fig. 1; and

Fig. 3 is a detail section illustrating the manner of attaching the pole pieces to the revolving field structure, as seen along the plane 3-3 of Fig. 1. a

In the present instance, the armature core I is shown as being made up of a series of laminations and appropriately supported by a frame 2. This frame 2 has the end housings 3 and 4, provided with feet 5. The shaft 6 is appropriately supported as by ball bearings, in the housings 3 and 4. The armature winding 1 is indicated in diagrammatic fashion only.

The field structure is supported upon the shaft 6 by the aid of a spider or hub 8, which may be pressed onto the shaft 6. This spider 8, as well as the pole pieces 9, can be formed of appropriate magnetic material such as mild steel, either cast or forged. Such mild steel may be of low carbon content, such as 20 points of carbon.

In the present instance the alternator is shown Each of the pole pieces is surrounded by a field coil i0. Excitation for the field can be obtained by way of the collector rings l2 and brushes I! in the conventional manner.

Each of the pole pieces 9 can be provided with a pole tip ii having an arcuate exterior surface. One of the important features of this invention resides in the fact that the air gap between the pole tipii and the armature structure I is of very low value; of the order of 2 or 3 thou-.

sandths of an inch per inch of radius of the revolving field. I

The manner in which the individual pole pieces '9 are fastened to the spider or hub 8 is such that a very low magnetic reluctance is provided at the joints. For this purpose, each of the pole pieces 9 may be provided with an inwardly radially extending projection ll. These projectionsfit very snugly into corresponding radial recesses l5 formed in the hub or spider 8; In order to lock the pole pieces in place, a transverse locking pin I6 can be used, which passes transversely across the recesses l5 and through the projections H. These locking pins are preferably made of low magnetic reluctance material, and should have a scription is not to be taken in a limiting sense, -tight fit in the apertures provided threfor.

66 Referring tothe drawing:

Surrounding each of the projections I there is a shoulder H on each of the pole pieces 9. This shoulder contacts snugly with'the corresponding surface of the spider 8, which is: formed with flat sides for this purpose. 4

It is seen that the area of contact between each of the pole pieces 9 and the corresponding area on the hub 8 is made quite *large, and an intimate contact is provided by accurate machining of the flat surfaces and of the cylindrical surfaces forming the projection i4 and the recess ii. In this way, a very low magnetic reluctance is provided g. the field core structure cooperate to reduce the 45 the order oftwo-thousandths of an inch to threeinherent effects of the armature reaction upon regulation. 1

What is claimed is:

1. In a definite pole alternator, an armature having a magnetic core, and a field structure cooperating with the armature and having a magnetic core, said field core having a series of pole pieces as well as a hub support for the pieces, said [hub support and pole pieces being joined by a radial projection extending from one of the ele- -ments into a closely contacting recess formed in the other element; there being a shoulder surface formed around the projection in intimate contact with the corresponding surface on the other element, to provide a tight joint at these surfaces, and the air gap between the pole pieces and the armature being of the order of two thousandths of an inch to three thousandths of an inch per inch of radius of the rotating element. F

2. In a definite pole alternator, an armature having a magnetic core, and afield structure cooperating with the armature and having a magnetic core, said field core having field-pole pieces forming an air gap with the armature core of thousandths of an inch per inch of radius of the also having a shoulder surface around the pro-'.

jections in intimate contact with the corresponding hub surfaces; said field core also having locking means extending across the recesses and through the projections and made from magnetic material, to hold the contacting surfaces in intimate relation to each .other.

3. A definite pole alternator having an armature core structure as well as a magnetic field structure with a central element and definite pole pieces attached thereto, one of the structures being rotatable, characterized by the fact that the air gapibetween /the structures is reduced to a value of the order of two and one half thou sandths of an inch per inch of radius of the rotating structure, and that the magnetic reluctance through the magnetic path including the pole pieces is further reduced to a very low value by ensuring a large and intimate contact between the pole piece surfaces that contact with the central element.

4. A definite pole alternator having an armature core structure as well as a magnetic field structure with a central element and definite pole pieces attached thereto, one of the structures being rotatable, characterized by the fact that the air gapbetween the structures is reduced to a value oi the order of two and one half thousandths of an inch per inch of radius of the r0.- tating structure, that each of the pole pieces and the central element are joined by the aid of a projection telescoping into and closely contactin substantially all surfaces of a corresponding recess, and that there is a shoulder surrounding the projection in intimate contact with the corresponding surface on the other element.

5. In an alternator, an armature core structure. and a fleld core structure, one of said structures being rotatable, said iield core structure having definite pole pieces and a hub supporting said pieces, the air gap between the structures being of the, order of three thousandths of an inch per inch oi radius of the rotating structure, and each of said pole pieces being joined to the hub so as to form large contacting surfaces between the pole piece and the hub and held in ciosecontacting relation to each other for reducing the mag etic reluctance through the definite pole stru ture. a

6. In an alternator, an armature core structure, and a field-core structure, one of said structures being rotatable, said field core structure having .deflnite pole pieces and a hub supporting said radial projection extending into a closely contacting recess, there being a shoulder surface formed around the projection and urged into intimate contact with the corresponding surface.

LEROY H. PALMER. 

